Explosively welded plug for leaky tubes of a heat exchanger and method of using the same

ABSTRACT

A plug for a leaky tube of a heat exchanger, the plug being weldable to the leaky tube by a shock wave propagated by an explosive charge disposed within the plug and a method of plugging a leaky tube by explosively welding the plug to the leaky tube.

O United States Patent 1191 1111 3,724,062 Cantrell et al. [4 1 Apr. 3,1973 54 EXPLOSIVELY WELDED PLUG FOR 3,543,370 12 1970 Berman et al...228/3 x LEAKY TUBES OF A HEAT 3,555,656 l/1971 Brown et al. ..29/470.1X

EXCHANGER AND METHOD OF USING 3,562,887 2/1971 Schroeder et a1.....228/3 X THE SAME 3,562,897 2/1971 Buchwald ..29/479 X 3,590,877 7/1971Leopold ..29/421 X [75] Inventors: Roger E. Cantrell; Louis A. Sturiale,

both of Tampa, Fla. OTHER PUBLICATIONS [73] Assignee: WestinghouseElectric Corporation, Gipson, Donald H., An Explosively Driven Pipe Clo-I Pittsburgh, Pa. sure, University of California Radiation Laboratory[22] Filed: Mar. 18 1971 Report 12203, TID4500 (37th Ed.), 4/65 [21]Appl. No.2 125,514 Primary ExaminerJ. Spencer Overholser AssistantExaminerRonald J. Shore 52 us. or. ..29/470.1, 29/479, 102/1, 9

138/89, 228/3 511 1m. 01. ..B23k 21/00 1 ABSTRACT [58] Field of Search..29/479, 470.1, 421 E 486 A 1 1 p ug for a leaky tube of a heatexchanger, the plug 29/4975"228/3 138/89 being weldable to the leakytube by a shock wave propagated by an explosive charge disposed Withinthe [56] References cued plug and a method of plugging a leaky tube byexplo- UNITED STATES PATENTS sively welding the plug to the leaky tube.

3,491,798 1/1970 Beshara ..29/421 X 10 Claims, 3 Drawing FiguresEXPLOSIVELY WELDED PLUG FOR LEAKY TUBES OF A HEAT EXCHANGER AND METHODOF USING THE SAME BACKGROUND OF THE INVENTION This invention relates toa method and plug for plugging a leaky tube in a heat exchanger and moreparticularly to a plug which is explosively welded to the insidediameter of the tube and a method of utilizing such a plug.

When the surfaces of two metals are caused to come into contact with ahigh relative velocity and with an included angle of collapse, theinteracting surfaces will become welded together. This type of weldinghas been utilized to provide cladding for low alloy steels and othermetals with some type of metal which is difficult to weld byconventional methods due to their physical or chemical, properties, suchas aluminum, stainless steel or tantalum. Explosive welding generallyemploys a cold bonding, plastic flow phenomenon, which allows a largenumber of similar or dissimilar metals to be strongly bonded togetherwithout elaborate surface preparation.

Tubular heat exchangers are utilized to transfer heat between two fluidsin processes in which it is undesirable to mix the fluids. Occasionallyone of the tubes springs a leak due to corrosion or due to latentdefects in the tube. Because it is very difficult or almost impossibleto replace a leaky tube without disassembling the heat exchanger, theends of the leaky tube are generally plugged by driving plugs of sometype into the tube. The simplest plug being a tapered bar, which isdriven into the tube with a hammer and seal welded thereto. However, todrive such plugs there must be sufficient room to swing the hammer andmake a seal weld and a workman must remain in close proximity to thetube and tube sheet for an extended period of time in order to properlyseal the plug. While this time is not extremely long, it becomescritical, when the area is radioactive as in plugging nuclear steamgenerator tubes so that some extremely rapid methodsuch as explosivewelding is advantageous. For additional information relating to pluggingtubes with explosive devices reference may be made to US. Pat. No.3,555,656 by Francis X. Brown and Samuel Wismer, J r., assigned to thesame assignee.

SUMMARY OF THE INVENTION In general a plug for an end of a leaky tube ofa heat exchanger made in accordance with this invention is formed from ametal capable of being welded to the tube by a shock wave propagated byan explosive charge. Such a plug comprises a forward portion adapted tocenter the forward end of the plug in the tube, a central portion havingan outer peripheral surface formed to provide generally equal spacingsbetween the peripheral surface and the tube, a rear portion having afrustoconical shape adapted to center the plug within the tube andposition the plug relative to the end of the tube and a central cavityhaving an axial opening which extends through the rear portion and thecentral portion of the plug and partially into the forward portion. Anexplosive charge is disposed in that portion of the cavity adjacent thecenter portion of the plug and a detonating cord is in communicationwith the explosive charge to detonate the explosive charge andexplosively weld the plug to the tube. This invention also includes amethod of utilizing such a plug to seal off one end ofa leaky tube.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of thisinvention will become more apparent from reading the following detaileddescription in connection with the accompanying drawings, in which:

FIG. 1 is a partial sectional view of a heat exchanger tube sheetshowing a plug made in accordance with this invention before beingexplosively welded to one end of a leaky tube;

FIG. 2 is a partial sectional view of a heat exchanger tube sheetshowing the plug explosively welded to the end of a leaky tube; and

FIG. 3 is a sectional view of a modified plug.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings in detail, FIG. 1 shows a heat exchanger tube sheet 1 having aplurality of tubes 3 extending therethrough. A plug 5 is disposed in theend of the central tube so that it may be explosively welded thereto.The plug isshown to comprise a forward portion 7 having a diameterslightly less than the diameter of the tube 3 to generally center theforward portion 7 of the plug 5 in the tube; a central portion 9 havinga neckdown section having a peripheral surface 11, which is generallyspaced an equal distance from the surface 13 of the tube 3; and a rearportion 15 having a frustoconical peripheral surface 17 which centersthe rear portion of the tube 3 and positions the plug 5 relative to theend of the tube so that the center portion of the plug is adjacent thetube sheet 1.

An axial bore 19 provides a cavity, which extends through the rear andcentral portion 15 and 9, respectively, and partially into the forwardportion 7.

An explosive charge 20, such as TNT or SWP-l (an explosive manufacturedby Trojan-US Powder Co. of Allentown, Pa. and others, is disposed in thecavity 19 adjacent the central portion 9, which has a relatively thinwall 21 of uniform thickness. The explosive charge 20 is contained bywadding 23 and 25. The forward wadding 23 blocks the forward portion ofthe cavity 19 and the rear wadding 25 blocks the rear portion of thecavity 19 confining the explosive charge to the central portion of thecavity 19.

A detonating cord or Primacord 27, such as a 25 or 50 grain per footCordeau detonating cord extends through the rear wadding 25 and is incontact with the explosive charge 20. A blasting cap 29 is taped to thedetonating cord 27 and electrically connected to an electric blastingmachine 30 via conductors L1 and L2. The electrical blasting machine 30,when activated, will detonate the blasting cap 29 to ignite thedetonating cord 27 and detonate the explosive charge 20 which propagatesa shock wave.

The peripheral surface 11 of the central portion 9 of the plug 5 isdisposed an equal distance from the tube 3 so that the shock wavepropagated by the detonation of the explosive charge will progress fromadjacent the rear portion 15 of the plug 5 to adjacent the forwardportion 7 of the plug 5. This causes expansion of the central portion 9of the plug 5 to initiate adjacent the rear portion and progress to theforward portion 7 in such a manner that the peripheral surface 11 of thecentral portion 9 of the plug 5 will progressively contact the innersurface 13 of the tube 3 at sufficiently high velocity so that there isplastic flow at the interface of the surfaces as they come into contactto provide a weld between these surfaces. The weld thus formed is strongand essentially free of voids and inclusions of foreign material, due toa jetting effect caused by the rapid collapse of the included anglebetween the interacting surfaces as the expansion of the thin wallportion 21 of the plug progresses.

FIG. 2 generally shows the shape of the plug 5 after it is explosivelywelded to the tube 3.

FIG. 3 shows a modification of the plug shown in FIG. 1. In the modifiedplug 5, the center and rear portions 9 and 15 respectively are generallythe same as the center and rear portions of the plug shown in FIG. 1.However, the forward portion 7' in the modified plug has a bore 31extending partially therein from the forward end thereof. Thus, leavinga solid metal plug 33 between the cavity 19 and the bore 31. The wall 35of the bore 31 has kerfs 37 spaced girthwise thereon to permit endsegments of the wall 35 to be flared outwardly to provide leaf springsfor centering the plug 5' within the tube 3 and holding the plug inposition prior to detonating the explosive charge. The rear portion 15of the plug 5 has a frustoconical peripheral surface so that the plugmay be made to a nominal size and yet centered accurately in tubeshaving openings which vary several thousandths in diameter to providegenerally uniform spacing between the central portion 9 of the plug 5'and the tube 3 to locate the plug relative to the end of the tube andfirmly hold the plug in place prior to explosively welding it to thetube.

A method of plugging a leaking tube utilizing a plug made in accordancewith this invention comprises the following steps;

identifying and marking the ends of the leaking tube;

cleaning inside one end of the leaking tube to a depth of approximately3 to 4 inches;

inserting a clean dry felt pad 39 into the end of the tube, pushing itto a depth slightly in excess of seven inches to provide a temporaryplug or dam to prevent water from seeping into the plugging area priorto explosively welding the plug 5 to the tube 3;

cleaning the plug 5 to remove all grease and foreign material; formingwadding 23 for the forward portion 7 of the plug by rolling masking tapeinto a cylinder, which fits snugly into the bore 19 of the plug 5;

inserting the wadding 23 into the bore 19 until it is slightly past thecentral portion 9 of the plug 5 approximately 2.4 inches into the plugsas shown in FIG. 1;

weighing out a predetermined amount of explosive material placing theexplosive material 20 in the bore 19 of the plug 5;

lightly tapping the forward portion 7 of the plug 5 on a table top tosettle the explosive;

cutting a length of detonator cord 27 sufficiently long to extend fromthe leaking tube 3, out a manway and to a position where the blastingcap 29 may be detonated outside of the heat exchanger; forming wadding25 for the rear portion 15 of the plug 5 by wrapping masking tape about3/32 inches from one end of the detonating cord 27;

inserting the tape wadding 25 and detonating cord 27 into the bore 19 ofthe plug 5 so that the detonating cord 27 comes into contact with theexplosive charge 20;

cleaning the outer peripheral surface of the plug 5;

coiling the detonating cord 27 so that it can be held in one hand withthe plug 5 and passed through a manway opening into the heat exchanger;

inserting the plug 5 in the end of the leaking tube 3;

pushing the plug into the tube until the frustoconical surface 17adjacent the rear end of the tube 3 contacts the tube;

ascertaining that there is no electrical source in the manway area whichcould prematurely ignite the detonating cord 27;

shoring the lead wires L1 and L2 adjacent the blasing machine 30;

fastening an electrically ignited blasting cap 29 to the detonating cord27 by taping it thereto with masking tape;

connecting the lead wires L1 and L2 to the blasting cap 29;

removing the short from the other end of the lead wires L1 and L2,checking that all personnel are out of the heat exchanger and away fromthe vicinity of the blasting cap 29;

firing the blasting cap 29 to ignite the detonating cord 27 and detonatethe explosive 20 to explosively weld the plug 5 to the tube 3;

inspecting the explosively welded plug 5 in the same manner as a fusionwelded plug would be inspected.

The other end of the leaking tube together with other leaking tubeswould be plugged in a similar manner. Such plugs may be welded to thetubing very rapidly and they also lend themselves to be inserted intoleaky tubes by remote control equipment, which is used to service heatexchangers utilized with nuclear reactors and associated steamgenerators.

What we claim is:

1. A plug for an end of a tube, said plug being formed of a materialcapable of being welded to said tube by a shock wave propagated by anexplosive charge, said plug comprising three integral portions,

a forward portion having means for centering said forward end of saidplug within said tube,

a central portion of reduced cross section having an outer peripheralsurface formed to provide generally equal spacing between said surfaceand said tube, and

a rear portion having a gradually increasing cross section to providemeans for centering said rear portion of said plug in said tube and forpositioning the plug relative to said end of said tube,

a central cavity formed by an axial opening of generally constant crosssection and extending completely through said rear portion and saidcenter portion and partially into said forward portion,

an explosive charge disposed in a portion of said cavity adjacent saidcenter portion of said plug, wadding disposed in said cavity to keepsaid explosive charge adjacent said center portion, and means fordetonating said explosive charge.

2. A plug as set forth in claim 1, wherein the material of the plug isessentially the same as the material of the tube.

3. A plug as set forth in claim 1, wherein the forward portion of theplug is generally cylindrical and has a diameter slightly smaller thanthe diameter of the tube.

4. A plug as set forth in claim 3, wherein the forward portion of theplug has an axial opening extending inwardly from the forward endthereof and a plurality of kerfs disposed in the forward end of the plugand spaced girthwise therein, and the forward end of the plug isexpanded outwardly to engage the tube for holding the plug in placeprior to explosively welding the plug to the tube.

5. A plug as set forth in claim 1, wherein the rear portion thereof isfrustoconical shape to provide the means for centering the rear portionof the plug and posi-tioning the plug relative to the end of the tube.

6. A plug as set forth in claim 1, wherein the central portion thereofhas a thin wall of uniform thickness,

said wall being substantially thinner than the walls of the forward andrear portions.

7. A method of plugging one end of a tube utilizing a plug having threeintegral portions, a forward portion, which has means for centering saidforward portion in said tube, a central portion of reduced cross sectionhaving an outer peripheral surface which is generally equally spacedfrom said tube when disposed therein and a rear portion which has agradually increasing cross section to provide means for centering saidplug in said tube and locating said plug relative to said end of saidtube, and a central cavity having an axial opening of generally constantcross section extending through said rear and central portions andpartially through said forward portion of said plug, said methodcomprising placing a forward wadding in said cavity so that said waddingplugs the cavity in the forward portion of the plug adjacent the centralportion,

placing a predetermined amount of explosive material in said cavity,

placing a rear wadding with detonating means extending therethrough insaid cavity to retain said explosive in the region of said centralportion of said plug,

inserting the forward end of said plug in said tube;

pushing the plug as far into the tube as it will go, and

detonating said explosive charge to explosively weld said plug to theend of said tube.

8. A method as set forth in claim 7 and further comprising cleaning theinside wall of the tube adjacent the end of the plug.

9. A methodas set forth in claim 7 and further comprising inserting atemporary plug into the tube to provide a dam to prevent liquid fromseeping into the area occupied by the plug prior to explosively weldingthe plug to the tube.

10. A method as set forth in claim 7 and further comprising cleaning theouter peripheral surface of the plug prior to inserting the plug in thetube.

1. A plug for an end of a tube, said plug being formed of a materialcapable of being welded to said tube by a shock wave propagated by anexplosive charge, said plug comprising three integral portions, aforward portion having means for centering said forward end of said plugwithin said tube, a central portion of reduced cross section having anouter peripheral surface formed to provide generally equal spacingbetween said surface and said tube, and a rear portion having agradually increasing cross section to provide means for centering saidrear portion of said plug in said tube and for positioning the plugrelative to said end of said tube, a central cavity formed by an axialopening of generally constant cross section and extending completelythrough said rear portion and said center portion and partially intosaid forward portion, an explosive charge disposed in a portion of saidcavity adjacent said center portion of said plug, wadding disposed insaid cavity to keep said explosive charge adjacent said center portion,and means for detonating said explosive charge.
 2. A plug as set forthin claim 1, wherein the material of the plug is essentially the same asthe material of the tube.
 3. A plug as set forth in claim 1, wherein theforward portion of the plug is generally cylindrical and has a diameterslightly smaller than the diameter of the tube.
 4. A plug as set forthin claim 3, wherein the forward portion of the plug has an axial openingextending inwardly from the forward end thereof and a plurality of kerfsdisposed in the forward end of the plug and spaced girthwise therein,and the forward end of the plug is expanded outwardly to engage the tubefor holding the plug in place prior to explosively welding the plug tothe tube.
 5. A plug as set forth in claim 1, wherein the rear portionthereof is frustoconical shape to provide the means for centering therear portion of the plug and posi-tioning the plug relative to the endof the tube.
 6. A plug as set forth in claim 1, wherein the centralportion thereof has a thin wall of uniform thickness, said wall beingsubstantially thinner than the walls of the forward and rear portions.7. A method of plugging one end of a tube utilizing a plug having threeintegral portions, a forward portion, which has means for centering saidforward portion in said tube, a central portion of reduced cross sectionhaving an outer peripheral surface which is generally equally spacedfrom said tube when disposed therein and a rear portion which has agradually increasing cross section to provide means for centering saidplug in said tube and locating said plug relative to said end of saidtube, and a central cavity having an axial opening of generally constantcross section extending through said rear and central portions andpartially through said forward portion of said plug, said methodcomprising placing a forward wadding in said cavity so that said waddingplugs the cavity in the forward portion of the plug adjacent the centralportion, placing a predetermined amount of explosive material in saidcavity, placing a rear wadding with detonating meAns extendingtherethrough in said cavity to retain said explosive in the region ofsaid central portion of said plug, inserting the forward end of saidplug in said tube; pushing the plug as far into the tube as it will go,and detonating said explosive charge to explosively weld said plug tothe end of said tube.
 8. A method as set forth in claim 7 and furthercomprising cleaning the inside wall of the tube adjacent the end of theplug.
 9. A method as set forth in claim 7 and further comprisinginserting a temporary plug into the tube to provide a dam to preventliquid from seeping into the area occupied by the plug prior toexplosively welding the plug to the tube.
 10. A method as set forth inclaim 7 and further comprising cleaning the outer peripheral surface ofthe plug prior to inserting the plug in the tube.